In electronic circuit systems, unwanted signals can lower the dynamic range of a system or damage it if the power level is high enough. Bandstop filters can be used (e.g., in radio frequency (RF) and microwave systems) to reject unwanted signals from entering a receiver or leaving a transmitter. For example, bandstop filters can be used in RF and microwave systems to remove unwanted signals over a specific frequency range while passing signals with frequencies that fall outside of that range. These unwanted signals can originate from co-site or externally generated interference as well as nonlinear components under high-power excitation in the system.
In applications where manually-switched bandstop filters are used to block expected interference, a delay is used so that the filter can be switched. In applications where they are used reactively to block unexpected interference, there is a processing delay during which the system determines that the filter needs to be switched.
Static and switched bandstop filters can be useful when the schedule and electrical characteristics of unwanted signals is known. However, in many modern scenarios, this information is not known by all of the systems that interact with one another in a given area. In some of these cases, limiters can be used to protect receivers from damaging unwanted signals.
Limiters can be placed into two broad categories: wideband and frequency-selective. Wideband limiters can protect receivers at the cost of attenuating signals at all frequencies, not just at or around frequencies that contain high-power signals. Frequency-selective limiters can provide high attenuation only around frequencies that contain high-power signals. However, previous implementations have other undesirable traits, such as moderately high attenuation of low-power signals. Additionally, frequency-selective limiters are generally not commercially available.
Features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.